Diseases of vegetable crops, in general, is an unpleasant thing, and when there are no special toxic chemicals to combat diseases, this does not add optimism to the majority of gardeners. Nevertheless, potato bacterial diseases can and should be learned to cope, as they are very common and can kill up to half or more of the annual harvest.
Ring rot of potatoes belongs to the number of bacterial diseases and is found everywhere in all areas where potatoes are grown. The disease is cunning because its symptoms develop rather slowly and are not immediately visible from the outside, although crop losses can be up to 40-45%. In this article you can find photos of signs of the disease, as well as its description and treatment methods. It is only necessary to immediately understand that in the case of ring rot treatment as such is usually not carried out. Infected plants are subject to immediate destruction - it is impossible to save them. But the prevention of the disease plays a very important role.
Signs of ring rot disease
The causative agent of ring rot are bacteria of the species Clavibacter michiganensis subsp. sepedonicum or in another way they are called Corynebacterium sepedonicum. Belong to a variety of aerobic bacteria.
Signs of the disease appear on the roots, tubers, stolons, and also the stalks and leaves of the potato are affected. Infection usually begins with tubers, but the first symptoms of the disease can be seen only when they are cut, so if the tubers are already sitting in the ground, then the disease can only be traced along the aerial part of the potato bush.Important! With a small defeat of the tubers, the first signs usually appear during the flowering period.
One or two stems wilt in the bush, and they quickly fall to the ground. This fall is already a characteristic sign of ring rot, as with other diseases (verticillis, fusarium) faded stems remain standing. Then brown spots appear on the tips of the leaves of withered stems. Sometimes the leaves of the affected stems may turn white due to the loss of chlorophyll.
The fact is that bacteria, moving from an infected tuber through the stolons to the stalks of the potato bush, accumulate there and cause the vessels to clog. As a result, nutrient fluids cannot enter the upper part of the plants, and the leaves first lose their turgor, and then wither. In addition, the pathogen releases toxic substances for potatoes.
As a result of significant damage to ring rot, the following symptoms are observed:
- The upper leaves of the whole bush begin to turn yellow and curl.
- The surface between the leaf veins acquires a fawn color, so the leaves become like speckled.
- The lower leaves of the bushes become sluggish and thin, their edges can curl upwards.
- The internodes are shortened, the potato bushes take on a dwarf appearance.
All these symptoms are well illustrated by the photos below.
If you cut off a diseased stem and place it in water, then light yellow mucus will clearly flow from it. At the same time, the affected stalks are not easily pulled out of the ground, since the vein structure of shoots and root crops is destroyed.Attention! The excretion in the process of decay of the yellow-pale yellow mucous mass is considered to be a diagnostic sign, according to which, among other diseases, it is the ring rot of potatoes that is isolated.
Potato tubers, still weakly infected, are virtually indistinguishable from healthy tubers in appearance. But if you make a cross-section, then the vascular ring can be observed yellowing and softening of the tissues of potatoes. In the photo below you can observe how ring rot of potatoes looks on a tuber in the initial phase of infection.
As the disease progresses, the vascular system of the potato begins to completely break down and turns into a slimy mass, which is squeezed when you press the tuber.
Two forms of the disease
There are two forms of damage to potato tubers by this disease: pitted rot and ring rot. Pitted rot is usually the primary form of this bacterial disease. Plants usually infect during the autumn period during harvest. At first, no signs of disease on the tubers can be noticed. The disease can begin to manifest itself only 5-6 months after storage, at the very beginning of spring. Under the skin, where the infection occurred, light spots are formed, no larger than 2-3 mm. Later they begin to grow and reach 1.5 cm. The flesh in these places begins to decompose and a fossa forms.
Attention! This form of the disease is often referred to as yellow subcutaneous spot.
If, in preparation for planting, such tubers are not tracked down and planted in the ground, the disease will begin to develop and the infection will pass to the tubers.
Ring rot infection usually occurs from old tubers, through stolons and necrosis of the vascular ring appear already on young tubers.
Conditions for the development of the disease
Since chemical measures to combat ring rot of potatoes do not exist, it is necessary to understand the sources of infection and conditions for the development of the disease as best as possible in order to understand what preventive measures should be taken in order to protect themselves as much as possible from this disease.
The ideal conditions for the development of the disease are moderate temperatures (from + 20 ° C) and high humidity. It should be borne in mind that at high temperatures and dry conditions, the development of the disease is suspended, and although the above-ground part of the plants quickly fade, it does not practically affect the tubers. They look quite healthy.
The main source of preserving the infection and transmitting it to the tubers of a new generation is already affected tubers. Unlike some other pathogens, ring rot bacteria do not persist in the soil and do not hibernate. But they may well be stored in unheated premises on any plant debris or garden tools and, of course, on stored tubers. In this case, healthy tubers can become infected by contact with affected specimens, especially if the first ones have peel damage, scratches, bare spots or cuts. That is why it is better to store all the cut potatoes separately from the main crop and to use them as soon as possible for their intended purpose.
Infection is also easily transmitted through tools when harvesting potatoes and especially when cutting tubers.
It is still difficult to fight the disease, because its pathogen is quite capable of moving from a tuber to a tuber for several generations without any visible symptoms, if suitable conditions for its development do not occur. Therefore, sometimes it turns out that planting apparently healthy tubers can get sick plants.
Ways to combat the disease
The main measures to combat ring rot include the following agricultural practices:
- The use of potato varieties resistant to this disease. When choosing the right variety, keep in mind that early potato varieties are most susceptible to ring rot.
- During the entire growing season, timely detection and removal of diseased plants.
- If you are seriously struggling with ring rot, then it is imperative to observe crop rotation and not return the potatoes to the same place earlier than after 3 years.
- Before storing the tubers for storage, the tubers must be dried well and heated for 2 weeks at temperatures of at least + 16 ° + 18 ° C to detect infected specimens.
- Mowing and killing potato tops in a week, another before harvesting reduces the risk of infection.
- Formalin processing of the storage before laying the tubers.
- Germination of seed potatoes in the light also allows you to identify infected tubers.
Many gardeners successfully fight bacterial and fungal diseases of potatoes, including ring rot, by planting siderats. Oats, rye, wheat, barley, maize, legumes, tobacco, and cabbage are best suited to be able to cope with pathogens. It is necessary to select fast-growing crops that are able to form a sufficient amount of green mass from harvesting potatoes to frosts. In early spring, the field intended for planting potatoes must be planted with mustard or oats. Before planting potatoes, siderats are mown, the ground is loosened and mixed with plant residues. Saprophytes developing in the soil can significantly slow down the development of bacteria.
Finally, you can try to apply some ready-made preparations to combat this disease. Both before planting and before storing seed potatoes for storage, it is possible to pickle with fungicides Maxim, Kvadris or the biological product Gamair.
Before planting, it makes sense to also pickle the tubers with TMTD.
As you can see, if you use all of the above tools and methods in the integrated protection, then even the ring rot of potatoes will not frighten you.